Rates of gestational diabetes have been increasing as more U.S. women enter pregnancy overweight. Moderate to severe cases of the condition have long been treated, but doctors have been uncertain whether women with mild increases in blood-sugar levels warrant additional care.

"Healthcare providers do not wish to over-treat women or unnecessarily alarm them, nor do they wish to impose extra costs, including self-glucose monitoring," said Dr. Mark Landon, the lead investigator and interim chairman of obstetrics and gynecology at Ohio State University Medical Center. But, it seems, action does need to be taken.

In a federally funded study, published Wednesday in the New England Journal of Medicine, researchers assigned 958 women with mild gestational diabetes -- all of whom were between 24 and 31 weeks pregnant -- to receive either diabetes treatment or no treatment. The treatment-group participants were counseled on diet and how to monitor their glucose and, if necessary, they received insulin.

Most of the babies were born at normal weights. However, in the treatment group, 7.1% of infants were too large -- defined as at or above the 90th percentile -- compared with 14.5% in the untreated group. Babies in the treated group also were less likely to be born via C-section or to suffer trauma at birth.

Women in the treated group gained less weight, had fewer preterm births and had fewer cases of preeclampsia, a sudden increase in blood pressure that can lead to premature delivery. The study was conducted at 14 sites nationwide and was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

"This study was important to point out that even mild diabetes that is well-controlled and well-monitored can make a difference and improve pregnancy outcomes," said Dr. Diane Ashton of the March of Dimes, who was not involved in the research.

The lower incidence of preeclampsia found in the treated group is noteworthy, she added. About 8% of the women in the treated group developed the condition compared with 13% in the control group.

"That implies that tighter glucose control can prevent some of the vascular complications that are seen during pregnancy," she said.

When women develop gestational diabetes, their fetuses receive more blood sugar than they need. The extra energy is stored as fat, so these babies tend to be heavier at birth. Not only does the extra weight create more problems at the time of delivery, such babies appear to have an increased risk of developing obesity and metabolic diseases later in life.

"Other data, in animal species, strongly suggests that diet modification during pregnancy can affect birth weight and potentially even the appetite centers of the brain," Landon said.